Many optical scanning applications where target distances can change rapidly require fast, accurate and automatic focusing systems. For example, a package scanning system, such as one used for reading postal bar code labels from surfaces of boxes or packages on a moving conveyor, must necessarily be capable of reading labels from boxes of all sizes. Since such system is based on an optical configuration which must quickly adapt to reading the bar code labels that are located at differing heights above the conveyor, a highly responsive optical reading system is required.
Typically, optical systems which must be capable of automatic focusing over a predetermined range of object distances utilize lens element separation changes to accomplish the required imaging on a fixed image plane. Electrical range detectors and controlling systems for operating the mechanical adjustments are part of the systems. In the world of commercial photography, automatic focusing cameras allow for focusing by the movement of the lens assemblies in relation to the location of a fixed image plane where the film would be located. Such mechanically adjustable lenses are bulky, having a high mass which drastically slows the response time of the focusing adjustment. While acceptable in the fields they were designed for, such systems are undesirable in modern needs for high speed detection and electronic reading capability for scanned optical information.
It is an object of this invention to present an apparatus and method which provides rapid focusing of an object onto an image plane.
It is a further object of this invention to present an apparatus and method that rapidly and automatically focuses images of objects located in object planes with sequential and rapid varying distances from the lens or receiving optics of the apparatus.
A further object of the invention is to provide an apparatus and method where the rapid automatic focusing of the optical receiving system occurs by moving the image plane in respect to the fixed optics or lens system.
Another object of the invention is to provide rapid focusing for objects located at differing distances from the lens of the viewing apparatus through the use of an automatic and rapid imager position adjustment relative to the image plane wherein the image of the object will be focused by the lens.